Image pickup apparatus and control method of the same

ABSTRACT

An image pickup apparatus includes an object detection unit configured to detect an object, a brightness value acquisition unit configured to obtain a brightness value of each division region of an object field, an object photometric-value generation unit configured to generate a photometric value of the object from information of the object and a brightness value of each division region, a region selection unit configured to select a high brightness region, and an exposure-control photometric-value generation unit configured to generate a photometric value used for an exposure control from a photometric value of the object and a photometric value of the high brightness region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus, and moreparticularly to an image pickup apparatus configured to provide exposurecontrol using a detection result of an object.

2. Description of the Related Art

Recent digital cameras are mounted with the face recognition technologyas part of the object recognition. This technology is effective to anautomatic recognition of a main object in an image to be photographed,and proper photography of the main object. For example, when a humanexists in an object field and turns his face on a camera, his face isrecognized by the face recognition function and determined to be a mainobject. Accordingly, the camera provides such automatic focus, whitebalance, exposure controls that the recognized face can be properlyphotographed. Japanese Patent Laid-Open No. (“JP”) 2003-107555 proposesa digital camera configured to generate a photometric value used for theexposure control by weighing a photometric value of a face recognitionpart and a photometric value of the entire object field.

Once the main face is determined in the face recognition, JP 2003-107555provides automatic exposure on the basis of the main face and may notprovide exposure control pursuant to the photographer's intent when themain face is not located at the photometric center. For instance, somerecent digital cameras have a photography mode (spotlight mode) used toproperly photograph a spotlighted object. In the spotlight mode, thehigh brightness region in the object field is searched and its region isproperly exposed. Hence, when the main face is automatically exposed inthe spotlight mode and there is no main face in the high brightnessregion, the high brightness region is excessively bright and a faceother than the recognized main face in the brightness region is notproperly exposed.

SUMMARY OF THE INVENTION

The present invention provides an image pickup apparatus that canphotograph with proper exposure an object in a high brightness area.

An image pickup apparatus according to one aspect of the presentinvention includes an image pickup device configured to convert incidentlight from a lens into an electric signal, an object detection unitconfigured to detect an object by extracting a characteristic point ofan image based on an output of the image pickup device, a brightnessvalue acquisition unit configured to obtain a brightness value of eachdivision region of an object field that is divided into a plurality ofdivision regions, an object photometric-value generation unit configuredto generate a photometric value of the object from information of theobject detected by the object detection unit and the brightness value ofeach division region obtained by the brightness acquisition unit, aregion selection unit configured to select a high brightness regionhaving a brightness value equal to or higher than a threshold in theobject field, and an exposure-control photometric-value generation unitconfigured to generate a photometric value used for an exposure controlfrom a photometric value of the object generated by the objectphotometric-value generation unit and a photometric value of the highbrightness region generated by the region photometric-value generationunit. When the object detection unit detects a first object in the highbrightness region, and a second object in a low brightness region thatis lower in brightness than the high brightness region and other thanthe high brightness region, the exposure-control photometric-valuegeneration unit uses the photometric value of the high brightness regiongenerated by the region photometric-value generation unit and thephotometric value of the first object generated by the objectphotometric-value generation unit to generate the photometric value usedfor the exposure control but without using the photometric value of thesecond object generated by the object photometric-value generation unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a digital camera (image pickup apparatus).

FIG. 2 is a plane view of an object field of the digital camera shown inFIG. 1.

FIG. 3 is a plane view of division regions made by dividing the objectfield shown in FIG. 2.

FIG. 4 is a plane view showing that a face becomes unrecognized in thehigh brightness area of the object field shown in FIG. 3.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a block diagram of a digital camera (image pickup apparatus)according to one embodiment of the present invention.

Reference numeral 110 denotes a lens used to image an object. Referencenumeral 120 denotes a stop mechanism configured to control an incidentlight quantity. Reference numeral 130 denotes a stop driving motorconfigured to drive the stop mechanism 120. Reference numeral 140denotes a stop mechanism driver configured to drive the stop drivingmotor 130. Reference numeral 150 denotes a stop state detectorconfigured to detect a state of the stop mechanism 120.

Reference numeral 200 denotes an image pickup device configured to(photoelectrically) convert the incident light from the imaging lens 110into an electric signal. Reference numeral 210 denotes an image pickupdevice driver configured to control the image pickup device 200, to readout the photoelectrically converted signal, and to control a so-calledelectronic shutter function that controls a signal accumulating timeperiod. Reference numeral 220 denotes a sample-and-hold/AGC circuitconfigured to sample the signal photoelectrically converted by the imagepickup device 200, and to electrically amplify the resultant signal.Reference numeral 230 denotes an analogue to digital (“A/D”) converterconfigured to convert an analogue signal as an output of thesample-and-hold/AGC circuit 220 to a digital signal.

Reference numeral 240 denotes a digital signal processor (“DSP”) thathas a control function configured to generate a standard televisionsignal in addition to a synchronization signal after a gamma correctionand other processes, such as a color separation and a color differencematrix. Reference numeral 240 a denotes an object detection unitconfigured to detect an object (face) in an image by extracting acharacteristic point based on digital data from the A/D converter 230.Reference numeral 240 b denotes a brightness value acquisition unitconfigured to acquire a brightness value of a field, and to obtain abrightness average value of the entire field and a brightness averagevalue for each of a plurality of division regions.

Reference numeral 250 denotes a memory configured to store an imageprocessed by the DSP 240. Reference numeral 260 denotes a recordingmedium configured to record a motion image and a still image.

Reference numeral 270 denotes a microcomputer configured to issue aprocessing instruction to the DSP 240. Reference numeral 280 denotes adisplay configured to display an image. Reference denotes 270 a denotesan object photometric-value generation unit configured to generate aphotometric value of an object detected by the object detection unit 240a from object information detected by the object detection unit 240 aand the brightness value obtained by the brightness value acquisitionunit 240 b. Reference numeral 270 b denotes a region selection unitconfigured to automatically select a brightness region that is a certainconstant brightness region, based on the brightness value obtained bythe brightness value acquisition unit 240 b. Reference numeral 270 cdenotes a region photometric-value generation unit configured togenerate a photometric value of a region selected by the regionselection unit 270 b. Reference numeral 270 d denotes anexposure-control photometric-value generation unit configured togenerate a photometric value used for the exposure control from both thephotometric value of the object generated by the objectphotometric-value generation unit 270 a and the photometric value of aselected region generated by the region photometric-value generationunit 270 c. Reference numeral 270 e denotes an exposure controllerconfigured to control exposure based on an output of theexposure-control photometric-value generation unit 270 d. The exposurecontroller 270 e determines which of the stop mechanism 120, theelectronic shutter, and the AGC is to be operated, and issues aninstruction to the stop mechanism driver 140, the image pickup devicedriver 210, the sample-and-hold/AGC circuit 220. Reference numeral 270 fdenotes a timer configured to measure a set time (period) T.

Referring now to FIGS. 2 and 3, a description will be given of exposurecontrol over a face (first object) of a human H1 when the face islocated at a spotlighted part. FIG. 2 is a schematic view of an objectfield and an upper left region A1 in the field is a high brightness areathat is spotlighted. The region A1 is more brightly irradiated than aregion A2 that is not spotlighted around the region A1. The region A2 isa low brightness area that is other than the high brightness region inthe object field, and a face (second object) of a human H2 exists on theright side in the field. The human H2 is larger than the human H1.

In calculating a photometric value Yh of the region A1, an object fieldS shown in FIG. 2 is divided into a plurality of division regions thatare expressed by a matrix having a transverse coordinate “i” and alongitudinal coordinate “j,” as shown in FIG. 3, and a brightness valueYij is obtained which indicates brightness of each division region perunit area. Reference symbols “i” and “j” satisfy 1≦i≦8 and 1≦j≦8,respectively, and are parameters indicating a position of each divisionregion. The brightness value of the upper left corner division regionhas a brightness value of Y11 and the brightness value of the lowerright corner division region has a brightness value of Y88. Themicrocomputer 270 compares this brightness value with a threshold Yth1and determines that the region is the high brightness region whendetermining that the brightness value is equal to or higher than thethreshold Yth1, as in the Equation 1:

Yij≧Yth1  EQUATION 1

In FIG. 3, division areas having coordinates (i, j) of (2, 1), (3, 1),(1, 2), (2, 2), (3, 2), (1, 3), (2, 3), (3, 3), (1, 4), (2, 4), (3, 4)meet the condition of the Equation 1. Therefore, the region selectionunit 270 b selects these division regions as first division regions.Next, the region photometric-value generation unit 270 c averagesbrightness values Y21, Y31, Y12, Y22, Y32, Y13, Y23, Y33, Y14, Y24, andY34 of eleven division regions and generates a photometric value Yh ofthe region A1 as in the equation below:

Yh=ΣYij (where i and j are coordinates that satisfy the condition of theEquation 1)  EQUATION 2

Next, the object photometric-value generation unit 270 a determineswhether a face is detected in the region A1, based on a detection resultof the object detection unit 240 a of the DSP 240. Initially, the objectphotometric-value generation unit 270 a detects the region A1 utilizingthe Equation 1 and the result of the brightness value acquisition unit240 b of the DSP 240, and stores in the memory 250 the coordinate (i, j)of the high brightness region which indicates the position of thedivision region(s) that satisfy the condition. In addition, the objectphotometric-value generation unit 270 a stores in the memory 250 acoordinate (if, jf) at which the face exists as a face recognitionresult of the object detection unit 240 a exists, and a photometricvalue Yf of the face per unit area obtained by the brightness valueacquisition unit 240 b. The object photometric-value generation unit 270a determines that the face exists in the region A1 when determining thatthe existence coordinate of the face stored in the memory 250 accordswith the region A1 stored in the memory 250. Otherwise, the objectphotometric-value generation unit 270 a determines that no face existsin the high brightness region.

FIG. 3 shows the humans H1 and H2 in the object field with both facesrecognized. Assume that the face of the human H2 has a photometric valueYf1 at an existence coordinate (6, 3) and the face of the human H1 has aphotometric value Yf2 at an existence coordinate (2, 2). When theexistence coordinates of these two faces are compared with thecoordinate of the region A1 stored in the memory 250, only the existencecoordinate (2, 2) of the face of the human H1 matches. In other words, aface of one person is recognized in the high recognition region and aface of another person is recognized in the low brightness region.

Here, the exposure-control photometric-value generation unit 270 dgenerates a photometric value Yt used for the exposure control utilizingthe above face recognition result and the following equation. Here,assume that Yh is the photometric value of the region A1, as discussedabove, and k1 and k2 are a numerator and a denominator of a coefficient,Nh is an emphasis ratio of the photometric value of the region A1, andN1 is an emphasis ratio of the photometric value of the face in theregion A1.

Yt=(k1/k2)×((Yh×Nh+Yf1×N1))/(Nh+N1)  EQUATION 3

Thus, the face of the human H1 in the region A1 can be photographed withproper exposure using the photometric value of the face of the human H1recognized in the region A1 but without using the photometric value ofthe face recognized in the region A2.

Referring now to FIG. 4, a description will be given of exposure controlover the face that has been recognized in the region A1 but becomesunrecognized due to a human action, a movement of the spotlight, etc.When the face that has been recognized in the high brightness regiondisappears, the photometric value used for the exposure control isexpressed as follows:

Yt=(k1/k2)×Yh  EQUATION 4

As soon as the face disappears in the high brightness region, theEquation 3 may be immediately shifted to the Equation 4 but the face mayagain appear in the high brightness region. Thus, when the facedisappears in the high brightness region with the exposure control basedon the result of the Equation 3 the exposure control follows based on aresult of the Equation 5 until a predetermined time period T elapsesafter the face disappears in the high brightness region. When the facedisappears in the high brightness region, a photometric value Yf1′ ofthe lastly recognized face in the high brightness region is stored inthe memory 250 and used for a calculation.

Yt=(k1/k2)×((Yh×Nh+Yf1′×N1))/(Nh+N1)  EQUATION 5

When the face is again recognized in the high brightness region beforethe time period T elapses after the recognized face disappears in thehigh brightness region, the exposure control is performed using thephotometric value of the recognized face and the result of the Equation3. When the face remains un recognized in the high brightness regionwhen the time period T elapses after the recognized face disappears fromthe high brightness region, the exposure control is performed based onthe photometric value of the high brightness region of the Equation 4.This control can provides stable exposure control when the objectbecomes undetected after the object has been detected in the motionimage photography, because the exposure does not change abruptly andsignificantly.

If the face remains unrecognized in the high brightness region after thetime period T elapses, the face recognition is performed in the lowbrightness region and the exposure control may be performed based on theEquation 6 and a photometric value Yf3 of the face of the recognitionresult, in order to emphasize the face detection result and to stabilizethe exposure.

When a plurality of faces recognized in the low brightness region, aface closest to the high brightness region is highly likely to be theface that has so far been used for the exposure control and thus thephotometric value of the face closest to the high brightness region maybe reflected more for the exposure control.

When there are a plurality of recognized faces in the low brightnessregion, the exposure control may be performed without reflecting aphotometric value of a face other than the face closest to the highbrightness region.

Yt=(k1/k2)×((Yh×Nh+Yf3×N1))/(Nh+N1)  EQUATION 6

When the face is again recognized in the high brightness region from theexposure control state based on the Equation 6, the exposure control maybe performed using the photometric value Yf1 of the face in the highbrightness region and the Equation 3. In this case, the Equation 6 isswitched to the Equation 3 after the time period T elapses after theface is again recognized in the high brightness region. Thereby, theexposure control becomes stable. When the face is not recognized both inthe high brightness region and in the low brightness region, thephotometric value of the high brightness region is for the exposurecontrol based on the Equation 4. Even in this case, after the timeperiod T elapses, the Equation 6 is switched to the Equation 4.

As described above, in the exposure control over the high brightnessregion in the object field, this embodiment provides exposure controlusing a photometric value of a high brightness region in the objectfield and a photometric value of an object detected in the highbrightness region in the object field. This configuration effectuatesproper exposure of the high brightness region in the object field. Inaddition, when the object becomes undetected after the object has beendetected in the high brightness region in the object field in the motionimage photography, the photometric value of the object just before theobject becomes undetected is continuously used for a predetermined timeperiod for the exposure control so as to stabilize the exposure control.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2008-296245, filed Nov. 20, 2008, which is hereby incorporated byreference herein in its entirety.

1. An image pickup apparatus comprising: an image pickup deviceconfigured to convert incident light from a lens into an electricsignal; an object detection unit configured to detect an object byextracting a characteristic point of an image based on an output of theimage pickup device; a brightness value acquisition unit configured toobtain a brightness value of each division region of an object fieldthat is divided into a plurality of division regions; an objectphotometric-value generation unit configured to generate a photometricvalue of the object from information of the object detected by theobject detection unit and the brightness value of each division regionobtained by the brightness acquisition unit; a region selection unitconfigured to select a high brightness region having a brightness valueequal to or higher than a threshold in the object field; and anexposure-control photometric-value generation unit configured togenerate a photometric value used for an exposure control from aphotometric value of the object generated by the objectphotometric-value generation unit and a photometric value of the highbrightness region generated by the region photometric-value generationunit, wherein when the object detection unit detects a first object inthe high brightness region, and a second object in a low brightnessregion that is lower in brightness than the high brightness region andother than the high brightness region, the exposure-controlphotometric-value generation unit uses the photometric value of the highbrightness region generated by the region photometric-value generationunit and the photometric value of the first object generated by theobject photometric-value generation unit to generate the photometricvalue used for the exposure control but without using the photometricvalue of the second object generated by the object photometric-valuegeneration unit.
 2. The image pickup apparatus according to claim 1,further comprising a timer configured to measure a set time period,wherein when the first object disappears in the high brightness regionbut the second object remains detected in the low brightness regionafter the object detection unit recognizes the first object in the highbrightness region, the exposure-control photometric-value generationunit generates the photometric value used for the exposure control byusing the photometric value of the high brightness region generated bythe region photometric-value generation unit and the photometric valueof the first object that has been lastly recognized, which has beengenerated by the object photometric-value generation unit but withoutusing the photometric value of the second object generated by the objectphotometric-value generation unit, until the timer measures the set timeperiod after the first object disappears in the high brightness region.3. The image pickup apparatus according to claim 2, wherein when thefirst object disappears in the high brightness region but the secondobject remains detected in the low brightness region after the objectdetection unit recognizes the first object in the high brightnessregion, the exposure-control photometric-value generation unit generatesthe photometric value used for the exposure control by using thephotometric value of the high brightness region generated by the regionphotometric-value generation unit but without using the photometricvalue of the second object generated by the object photometric-valuegeneration unit, after the timer measures the set time period after thefirst object disappears in the high brightness region.
 4. The imagepickup apparatus according to claim 2, wherein when the first objectdisappears in the high brightness region but the second object remainsdetected in the low brightness region after the object detection unitrecognizes the first object in the high brightness region, theexposure-control photometric-value generation unit generates thephotometric value used for the exposure control by using the photometricvalue of the high brightness region generated by the regionphotometric-value generation unit and the photometric value of thesecond object generated by the object photometric-value generation unit,after the timer measures the set time period after the first objectdisappears in the high brightness region.
 5. The image pickup apparatusaccording to claim 3, wherein after the first object disappears in thehigh brightness region and the object detection unit again recognizesthe first object in the high brightness region, the exposure-controlphotometric-value generation unit generates the photometric value usedfor the exposure control that has been so far generated by the regionphotometric-value generation unit until the timer measures the set timeperiod after the first object is recognized in the high brightnessregion.
 6. A control method of an image pickup apparatus, said methodcomprising: an object detecting step of detecting an object byextracting a characteristic point of an image based on an output of animage pickup device of the image pickup apparatus; a brightness valueacquisition step of obtaining a brightness value of each division regionof an object field that is divided into a plurality of division regions;an object photometric-value generating step of generating a photometricvalue of the object from information of the object detected by theobject detecting step and the brightness value of each division regionobtained by the brightness acquisition step; a region selecting step ofselecting a high brightness region having a brightness value equal to orhigher than a threshold in the object field; and an exposure-controlphotometric-value generating step of generating a photometric value usedfor an exposure control from a photometric value of the object generatedby the object photometric-value generating step and a photometric valueof the high brightness region generated by the region photometric-valuegenerating step, wherein when the object detection unit detects a firstobject in the high brightness region, and a second object in a lowbrightness region that is lower in brightness than the high brightnessregion and other than the high brightness region, the exposure-controlphotometric-value generating step uses the photometric value of the highbrightness region generated by the region photometric-value generatingstep and the photometric value of the first object generated by theobject photometric-value generating step to generate the photometricvalue used for the exposure control without using the photometric valueof the second object generated by the object photometric-valuegenerating step.